Many patients report a subjective feeling of worsening respiratory status during different times of the year, attributed to changes in weather. There is very little objective data to confirm the presence or absence of a seasonal variation in lung function. This study aims to examine the seasonal effect on the major indices of pulmonary function tests.
In a New York City pulmonary function laboratory of an academic medical center, 4486 pulmonary function tests (PFT) were performed during the period of 3/1997-5/2002. We divided the tests into four groupings, based on three month intervals corresponding to the respective seasons: Winter: January-March (N=1118), Spring: April-June (N=1281), Summer: July-September (N=1080), Autumn: October-December (N=1007). The mean forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), total lung capacity (TLC) and diffusing capacity for carbon monoxide (DLCO) values were entered for each of the 4 groups along with the FEV1/FVC ratio and the percentage of predicted values for FEV1, TLC and DLCO.
There was a significant decrease in the absolute and predicted FEV1 in the July to September grouping (Fig 1). This was accompanied by a decrease in the FEV1/FVC ratio (Fig 2) and the predicted DLCO during the same period. No significant change in TLC was found.
The data shows FEV1 and DLCO are significantly decreased during the summer months of July to September. This may explain some of the changes in symptoms experienced by patients.
This study demonstrates that in areas with four distinct seasons, lung function declines during the summer months. Further research into the reasons for the reduction in lung function seen in the PFT results may be indicated.
Paul Strachan, None.